1. Field of the Invention
The present invention relates to a flatness measurement apparatus for measuring a flatness of a surface of an object.
2. Description of the Related Art
For example, it is necessary to periodically measure a flatness of a wafer stage, containing a heater therein, which is installed in a closed vessel defining a vacuum or processing chamber of a chemical vapor deposition (CVD) apparatus. Whenever the flatness measurement of the wafer stage is carried out, the closed vessel is dismantled so that the wafer stage is taken out of the closed vessel, and then the wafer stage is set in a flatness measurement apparatus for the flatness measurement of the wafer stage. When the measured flatness of the wafer stage is acceptable, it is again assembled in the closed vessel. It takes approximately five or six hours for the dismantlement of the closed vessel to take out of the wafer stage therefrom, and thus there is a demand for a movable-type flatness measurement apparatus which is constituted such that a flatness measurement for the wafer stage can be carried out fast without taking the wafer stage out of the closed vessel.
Conventionally, the flatness measurement apparatus is constructed as an immovable-type flatness measurement apparatus, which is fixedly installed on a base or table on a floor. Usually, this immovable-type flatness measurement apparatus includes a stand on which an object to be measured is placed; and an X-Y stage on which a flatness-detection sensor is mounted. The X-Y stage is moved along an X-axis and Y-axis perpendicularly intersecting with each other, so that a surface of the object can be scanned all over with the flatness-detection sensor, whereby a flatness of the surface of the object can be measured. The X-Y stage occupies a large space due to the movement of the X-Y stage along-both the X-axis and the Y-axis, resulting in a bulkiness of the whole of the immovable-type flatness measurement apparatus.
In particular, for example, an extent of the movement of the X-Y stage along the X-axis must be from 1.3 to 1.5 times a maximum dimension of the object which should be scanned with the flatness-detection sensor along the X-axis. This is true for an extent of the movement of the X-Y stage along the Y-axis. Namely, the X-Y stage is very bulky. Thus, it is inexpedient to reconstitute this immovable-type flatness measurement apparatus as a movable-type flatness measurement apparatus is due to the bulkiness of the X-Y stage.
JP-A-2003-075147 discloses a second prior art immovable-type flatness measurement apparatus for simultaneously measuring flatnesses of both surfaces of a silicon wafer, and includes three needle-like supports for supporting the silicon wafer. Namely, the silicon wafer rests on the tips of the three needle-like supports. Also, this second prior art immovable-type flatness measurement apparatus includes a lifting/rotating mechanism for lifting and rotating the silicon wafer, and a pair of upper and lower flatness-detection sensors, which are held so as to be opposed to each other, with the silicon wafer being intervened between the upper and lower flatness-detection sensors.
In a flatness measurement, the silicon wafer is scanned with the upper and lower flatness-detection sensors by diametrically moving these sensors with respect to the silicon wafer, and thus flatnesses of both the surfaces of the silicon wafer are simultaneously measured along a diameter of the silicon wafer. Then, by using the wafer lifting/rotating mechanism, the silicon wafer is lifted from the tips of the needle-like supports, and is rotated by a predetermined angle. After the rotation of the silicon wafer by the predetermined angle, the silicon wafer again rests on the tips of the three needle-like supports. Subsequently, the silicon wafer is further scanned with the upper and lower flatness-detection sensors by diametrically moving them with respect to the silicon wafer, and flatnesses of both the surfaces of the silicon wafer are simultaneously measured along another diameter of the silicon wafer.
These diametrical flatness measurements are repeated whenever the silicon wafer is lifted and rotated by the wafer lifting/rotating mechanism, whereby both the surfaces of the silicon wafer can be scanned all over with the upper and flatness-detection sensor, whereby flatnesses of both the surfaces of the object can be measured.
By using the second prior art flatness measurement apparatus, it is impossible to carry out the flatness measurement of an installed object, e.g. the wafer stage installed in the vacuum or processing chamber of the CVD apparatus. Also, it is inexpedient to reconstitute the second prior art immovable-type flatness measurement apparatus as a movable-type flatness measurement apparatus due to a bulkiness of the wafer lifting/rotating mechanism.